The present invention relates to a motor vehicle drive arrangement including a locomotive drive train for transmission of drive torque from a locomotive drive engine to a locomotive drive transmission, at least one liquid pump for supplying at least one drive part with operating liquid, and a first pump drive connection from a rotary part of the locomotive drive train to the liquid pump. The rotary part of the locomotive drive train is a drive shaft which is drive-connected or drive-connectable to the locomotive drive transmission. Such an arrangement also includes an electrical machine capable of being operated as an electric motor and having a rotor which is drive-connected or drive-connectable to the liquid pump by way of a second pump drive connection, a first free-wheel in the first pump drive connection, the liquid pump being capable of being driven by the electric motor by way of the second pump drive connection more rapidly than by the rotary part of the locomotive drive train, without the rotary part being passively taken up, and a second free-wheel in the second pump drive connection, so that the liquid pump can be driven more rapidly by the rotary part than by the electric motor, without the rotor of the electric motor being passively taken up.
Accordingly, the invention relates to a motor vehicle drive arrangement having a locomotive drive train for transmission of drive torque from a locomotive drive engine to a locomotive drive transmission, at least one liquid pump for supplying at least one drive part with operating liquid, and a first pump drive connection from a rotary part of the locomotive drive train to the liquid pump.
A motor vehicle drive arrangement of this type is known from German publication DE 198 10 374 A1. In this arrangement, an oil pump is drive-connected or drive-connectable to an electrical machine via a first free-wheel and to an electric motor via a further free-wheel. The electrical machine is connected to the locomotive drive train via a planetary transmission and is capable of being operated as a starter for driving an internal combustion engine of the locomotive drive train and for the generation of torque in addition to the internal combustion engine. German publication DE 199 23 316 A1 shows free-wheels, arranged coaxially to an engine drive shaft, for starting an internal combustion engine and for driving an oil pump by means of an electrical machine. The oil pump is also capable of being driven by the locomotive drive train by means of a centrifugal clutch. German publication DE 100 12 385 A1 shows a liquid pump coaxial to a transmission drive shaft. German publication DE 695 10 897 T2 shows an electrical machine coaxial about a transmission shaft. Technological background information is also given in DE 199 17 665 A1 and German publications DE 43 42 233 A1.
In view of increasing requirements for the reduction of consumption and emission, in the future, it will no longer be possible to dispense with a start/stop operation of the internal combustion engine during brief interruptions in the travel of the motor vehicle, in particular at traffic-light intersections.
In order to achieve a rapid and yet comfortable starting of the internal combustion engine, starter/alternator units and various hybrid systems suitable for this purpose are being developed. Hybrid drives for motor vehicles are shown, for example, in German publication DE 40 04 330 C2, German laid-open publication DE 24 36 546 and German publication DE 40 05 623 A1.
The transmissions and, depending on the design, also locomotive drive clutches outside the transmission require, for lubrication and/or for their actuation, operating liquid which is generally designated as oil, even when this is often no longer oil nowadays. Accordingly, the liquid pumps necessary for this purpose are conventionally designated as oil pumps. The liquid pump or oil pump of an automatic transmission (automatically shiftable transmission) is driven, in the series production situation, via the pump impellor of a hydrodynamic torque converter. This pump impellor, in the series production situation, is coupled to the crankshaft of the internal combustion engine. Consequently, with the internal combustion engine switched off, the transmission-oil pressure (for shifting and lubrication of multiple-disc clutches or other clutches in the automatic transmission and/or of one or more shiftable clutches preceding the latter) cannot be maintained. This presents problems during the start/stop operation of the internal combustion engine, since a rapid “drive-on” of the vehicle is not possible. It is necessary here, for the vehicle to drive on, to wait until the transmission-oil system is filled after the start of the internal combustion engine and a sufficiently high pressure level for shifting the clutches of the clutch system has been established in the transmission-oil system. This is in contradiction to the desire for a rapid drive-on of the motor vehicle, for example after a stop and a subsequent start at a road intersection (demand for comfort), and consequently, in the event of start/stop operation, the oil supply has to be maintained by means of an additional external oil pump. This additional external oil pump conventionally consists of a pump and of an electrical drive machine and, because of the large amount of space which it requires, can hardly be accommodated in present-day motor vehicles.
Efforts to integrate hybrid systems in the locomotive drive train and/or to replace the hydrodynamic torque converter of the automatic transmission by the hybrid system lead to the same set of problems which are that no transmission-oil pressure or insufficient transmission-oil pressure can be generated when the transmission input shaft, which may serve for driving the oil pump, is stationary or is running at only a low rotational speed. Thus, even where hybrid systems are concerned, there is still the demand for an additional oil supply of the automatic transmission in specific operating situations, particularly during start/stop operation. Start/stop operation is desirable for energy saving not only at traffic-light intersections, but also in the case of buses at bus stops.
The problem that there is not sufficient transmission oil and/or not a sufficient transmission-oil pressure or pressure for main clutches of the motor vehicle in order to start the motor vehicle quickly arises not only in the case of vehicle drives of an internal combustion engine, but also in the case of vehicle drives which have another locomotive drive engine instead of an internal combustion engine, for example an electric motor which, for example, is supplied with electrical energy by a fuel cell. Here, too, for shifting a main clutch of the vehicle drive train and/or shift clutches and shift brakes in an automatically shiftable automatic transmission, it is necessary to have sufficient operating liquid, for example oil, and a sufficient liquid pressure in the transmission or the clutches and their control lines, where appropriate even during or before the starting of the motor vehicle.
One object of this invention is to provide in a simple and cost-effective way, and while taking up only a small amount of construction space, a solution in which, as far as possible simultaneously with the desire to start a motor vehicle, there is the operating-liquid pressure necessary for this purpose.
This object is achieved, according to the invention, by providing an electrical machine capable of being operated as an electric motor, having a rotor which is drive-connected or drive-connectable to the liquid pump by means of a second pump drive connection, and providing a first free-wheel in the first pump drive connection, the liquid pump being capable of being driven by the electric motor by means of the second pump drive connection more rapidly than by the rotary part of the locomotive drive train, without this rotary part being passively taken up. The first free-wheel surrounds the drive shaft coaxially and has a free-wheel part connected fixedly in terms of rotation to the latter, a hollow intermediate shaft, through which the drive shaft extends axially, is provided, each of a further free-wheel part of the first free-wheel and a free-wheel part of the second free-wheel is connected fixedly in terms of rotation to the intermediate shaft, and a further free-wheel part of the second free-wheel is connected fixedly in terms of rotation to the rotor of the electric motor. According to a free-wheel principle, each of the free-wheel parts free-wheel drives the other in one direction of relative rotation and does not drive the other in an opposite direction of relative rotation.
Further features of the invention are reflected in dependent claims.
The invention has the advantage that the full operating-liquid pressure is already present in the drive system during the start of a motor vehicle or in fractions of seconds thereafter. A further advantage of the invention is that, to achieve the object, a pump already present even in series production vehicles with an automatic transmission can continue to be used and can be used at the same point as hitherto and is sufficient as the sole pump, in that the latter can, if required, be driven electrically, irrespective of the operating state of the locomotive drive engine.
This means that only a single pump is required, which can be operated selectively by the locomotive drive engine (internal combustion engine or electric motor or other type of engine) or by an additional electrical machine which can be operated as an electric motor. This additional electrical machine may, if desired, be used as a generator for current generation, for example as a brake generator, at operating times when it is not required as an electric motor. Since the pump already present in series production vehicles can be used, it can, for example, continue to remain accommodated in a torque converter bell of an automatic transmission where it is already arranged even in known motor vehicles which do not have an additional electrical machine as an alternative drive for the oil pump. Furthermore, according to the invention, the external oil pump necessary hitherto in conjunction with start/stop operation or in the case of hybrid drive systems is not needed.
This means that, whenever the rotational speed of the transmission input shaft is too low in start/stop systems, the liquid pump (oil pump) can be operated by means of the electrical machine additionally integrated in the transmission case. This takes place, in the invention, via at least one free-wheel or, according to a preferred embodiment, via two free-wheels in the pump drive. As soon as the internal combustion engine or the transmission input shaft (which can be driveable by the internal combustion engine or by a hybrid system) rotates more rapidly than the additional electrical machine, the liquid pump can be operated by the transmission input shaft. When the transmission input shaft is at a standstill or is running at a low rotational speed, the electrical machine can, as an electric motor, drive the pump, without torque being transmitted to the transmission input shaft (and a converter or the locomotive drive transmission). The liquid-pressure supply of the automatic transmission is thus always ensured even when the rotational speed of the converter or of the transmission input shaft is not sufficiently high.
The invention is described below by means of preferred embodiments as examples, and with reference to the drawings.